二叉树的最小深度

class Solution {
public:
    int minDepth(TreeNode* root) {
        if(!root)return 0;
        return dfs(root);
    }

    int dfs(TreeNode*root){
        if(!root->left&&!root->right)return 1;
        if(root->left&&!root->right)return 1+dfs(root->left);
        else if(!root->left&&root->right)return 1+dfs(root->right); 
        else return 1+min(dfs(root->left),dfs(root->right));
    }
};